Embodiments of the present disclosure relate to a motor assembly, and more particularly to a motor assembly having an interior permanent magnet (IPM) motor and a driver unit configured to determine an angular position of a rotor of the IPM motor.
Electric machines such as permanent magnet synchronous motors have been used in variety of applications, including but not limited to electric pumps, electric or hybrid vehicles, as well as home and industrial appliances that employ rotary components, traction motors, and the like. Types of the permanent magnet synchronous motors may include surface permanent magnet (SPM) motors and the IPM motors. A permanent magnet synchronous motor typically includes a stator having stator winding including one or more phases, and a rotor having permanent magnets. The rotor may be disposed within the stator. Typically, to operate the permanent magnet synchronous motors, it is desirable that the phases of the stator winding are operated in a predetermined sequence. Therefore, it is desirable to determine an angular position of the rotor (hereinafter referred to as a “rotor position”) in order to determine voltage and/or current that is to be applied to the stator winding.
Some of the currently available systems employ one or more position sensors and/or encoders along with the permanent magnet synchronous motor to determine the rotor position. Sometimes, an operation of the position sensors and/or encoders is unreliable under certain harsh conditions including, but not limited to, increased temperatures (e.g., at the temperatures of about a few hundreds of degree centigrade). Further, the position sensors and/or encoders occupy additional space. Consequently, resulting motor assemblies employing such position sensors and/or encoders are not as compact. Moreover, use of the position sensors and/or encoders results in costly motor assemblies.
Further, some systems entail using a third harmonic of a back-electromotive force (EMF) generated by a motor to estimate the rotor position. However, in case of motors, such as the IPM motors which have saliency in the rotor, the back-EMF may vary with variations in load. More particularly, the third harmonic of the back-EMF is affected by the load variations. Especially, a phase angle of the third harmonic, which is indicative of the rotor position, is altered due to the load variations. Consequently, use of information corresponding to the third harmonic is unreliable for determining the rotor position of the IPM motors.